1. Field of the Invention
The present invention relates to a riserless well intervention system. In particular, the present invention relates to a subsea well intervention system having a surface injector and a snubbing jack at the subsea well without a riser. The present invention also relates to dynamic control of the subsea snubbing jack in a subsea well intervention system.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98.
Well intervention is work performed on a well other than drilling. To manage the working life of a well, a well intervention can adjust production levels, modify the well, detect well conditions or perform other tasks in order to extend the working life of the well. Well intervention requires safely entering the well, which may be pressurized and actively producing. Drilling rigs have been used in conventional well intervention systems. A coiled tubing injector is mounted on a drilling rig to insert coiled tubing into the well.
Subsea wells present different problems because environmental conditions do not allow for ease and accessibility of the components of a conventional well intervention system. A surface injector on a rig or vessel on the ocean surface supplies and delivers the tubular member, such as coiled tubing. The ability to erect a rig or riser above a subsea well is limited and expensive. Dynamic positioning (DP) technology enables a vessel on the surface to reliably engage the subsea well for a riserless intervention system. When the subsea wellbore on the ocean floor is located thousands of feet away from the riserless system on a vessel at the surface, controls of the surface injector on the ocean surface must account for both surface conditions and subsea floor conditions at the same time. However, changes at the surface location do not correspond directly to conditions at the subsea location, and the translation of the effects of changes at the surface location can be distorted in the translation along the tubular member extending to the subsea location.
In the past, various well intervention systems have been developed. U.S. Pat. No. 6,854,520, issued to Robichaux on Feb. 15, 2005, describes an apparatus and method for handling a tubular in a conventional well. The disclosed components of a tubing injector and a snubbing jack for regular wells on land.
For subsea wells, U.S. Pat. No. 7,438,505, issued to Olsen on Oct. 21, 2008, teaches a prior subsea well intervention system mounted on a rig or riser. The riser has the pipe handling systems for injecting into the well, when the riser is directly aligned above the well. These conventional subsea well intervention systems require a heave compensation device to account for movement of the riser on the ocean surface.
Riserless systems have also been developed to remove the expense of a rig or riser as a large floating platform over the well. U.S. Pat. No. 8,720,582, issued to Portman on May 13, 2014, and U.S. Pat. No. 9,151,123, issued to Portman on Oct. 6, 2015, both disclose related systems and methods for providing tubing to a subsea well. The heave of the vessel and the devices to supply tubing and to inject tubing at the subsea well are disclosed. The systems use two injectors with heave compensation between the two injectors.
Injectors of these prior art system, including the riserless systems, have limitations. The injector controls the delivery and direction of tubing through the well and provides the thrust to snub into the well against pressure. A prior art injector is shown as FIG. 1 based on U.S. Pat. No. 5,309,990, issued to Lance on May 10, 1994. Two chain drives with gripper elements engage an entire length of the cylindrical tubing. There are multiple components and moving parts, which require a large amount of power. Components for the chain rotation motors, chain tensioning, chain gripping force and the necessary circuitry are necessary elements of an injector. In addition to the high amount of power requirement, there is a greater risk of failure due to the number of components and circuitry involved. There are several moving parts, and there is a lot of coordination necessary. Adding the subsea conditions, the problems are increased. The expense and equipment to deliver the necessary power, such as hydraulic power, to a subsea injector is increased. The ability to repair and maintain the chain drives in such a remote subsea location is difficult and expensive. Not all repairs can be performed by remote operated vehicles (ROVs) or in underwater conditions. An injector having an independent control or slave control still includes the lack of durability and extra weight of multiple components.
A snubbing jack or snubbing unit is another oilfield tool conventionally used to assist in the insertion of a tubular member into a wellbore. Tubular members can include conventional pipe, coiled tubing, and wireline. The wellbore is pressurized, so force can be required to push the tubular member. In “pipe light” conditions, the pressure of the wellbore is sufficient to resist the insertion of the tubular member. The snubbing jack provides the force to push the tubular member against the pressure of the wellbore. In “pipe heavy” conditions, the length of tubular member already in the wellbore has sufficient weight to accelerate the insertion of the tubular member. The snubbing jack provides the force to resist the pull on the tubular member by the length already within the wellbore.
In cooperation with an injector, the snubbing jack provides the additional thrust and energy for the insertion into and extraction from the well. For example, both cited prior art references, U.S. Pat. No. 6,854,520 and U.S. Pat. No. 7,438,505, disclose a tubing injector and a snubbing jack in cooperation with the tubing injector. For the prior art subsea well intervention, a riser is required, and the snubbing jack is located at the surface. U.S. Pat. No. 6,854,520 recognizes the need for the heavy components and multiple components on a floating platform aligned above the well in order to provide the necessary thrust to the well.
For a riserless subsea well intervention, injector weight and reliability remains a problem. Riserless systems, such as U.S. Pat. No. 8,720,582 and U.S. Pat. No. 9,151,123, manage the multiple components with master injector and slave injectors. Although the weight and power consumption of a slave injector can be less than the weight and power consumption of a master injector, the slave injector still remains an injector with the inherent problems of an injector, such as multiple components, weight, reliability, durability and accessibility when located at a subsea location.
It is an object of the present invention to provide a system for riserless subsea well interventions.
It is an object on the present invention to provide a system for riserless subsea well interventions without a subsea injector.
It is an object on the present invention to provide a system for riserless subsea well interventions having a surface injector and a subsea snubbing jack.
It is an object on the present invention to provide a method for dynamic control of the subsea snubbing jack for inserting a tubular member into a subsea well from a surface injector without a riser.
It is another object on the present invention to provide a dynamic riserless subsea well intervention system with a subsea snubbing jack and a subsea hydraulic power unit and surface controls through an electric umbilical.
It is another object on the present invention to provide a subsea snubbing jack with traveling slips and hydraulic actuation of the traveling slips in a dynamic system according to well conditions.
It is another object on the present invention to provide a subsea snubbing jack with a gripping force sufficient for inserting tubular members in “pipe light” conditions and “pipe heavy” conditions and conditions between “pipe light” and “pipe heavy” conditions.
It is another object on the present invention to provide a subsea snubbing jack with a subsea hydraulic power unit responsive to speed control of the surface injector.
It is still another object on the present invention to provide a subsea snubbing jack in a riserless well intervention resistant to cavitation.
It is still another object on the present invention to provide a subsea snubbing jack in a riserless well intervention and an ROV backup for the snubbing jack.
It is still another object on the present invention to provide a subsea snubbing jack in a riserless well intervention operated through a moon pool of a vessel.
These and other objects and advantages of the present invention will become apparent from a reading of the attached specification and appended claims.